1. Field of the Invention
The present invention relates to a nonaqueous electrolyte secondary battery.
2. Description of the Prior Art
In consideration of the recent prevalence of portable electric appliances such as cellular telephones, notebook-type personal computers, or the like, there has been a promotion in the development of those batteries which can meet the demand for making these appliances be miniaturized and be provided with a high capacity. Among such batteries, the lithium ion secondary battery (hereinafter, sometimes simply referred to as “a battery”) is expected to meet such a demand since the lithium ion secondary battery has a high operating voltage and a high energy density.
Incidentally, since a lithium ion secondary battery is required to have such a high energy density as described above, a variety of mechanisms are adopted for the purpose of securing the safety of the battery in connection with its uses. In particular, a separator having a function to shut down at high temperatures, a PTC device increasing in resistance with increasing temperatures, or the like are available.
However, in a larger-sized secondary battery having a larger capacity, the chemical energy quantity which is stored in the battery becomes larger, and hence it is more important to secure the safety.